1. Field of the Invention
The present invention relates to an apparatus and method for aligning flexible printing plates and for accurately drilling pin register holes therein. More particularly, the invention relates to such an apparatus and method including a three-way adjustable table top assembly for mounting the plate, a stereomicroscope viewer for aligning the plate on the table by sighting pin register hole markings and a drill for drilling the pin register holes once the plate is properly positioned.
2. Description of the Related Art
In flexographic printing presses, flexible printing plates with a raised pattern including a design and/or printed message thereon are adhered to a press plate cylinder, which is positioned adjacent to a backup impression cylinder. Printing ink is applied to the raised design on the plate cylinder and paper to be printed is then pulled between the impression cylinder and the plate cylinder, resulting in an inked imprint of the raised design on the paper.
In order for the press to apply the inked design correctly to the paper, the flexible plate must be precisely aligned on the plate cylinder. This is typically done via pin register holes punched in the flexible plates which are fitted over register pins on a press plate cylinder. In U.S. application for patent Ser. No. 08/266,128 entitled SYSTEM AND APPARATUS FOR PROVIDING PIN REGISTER HOLE MARKINGS ON FLEXIBLE PRINTING PLATES AND APPARATUS AND METHOD FOR ALIGNING PLATES ON A FLEXOGRAPHIC PRINTING PRESS PLATE CYLINDER, filed Jun. 27, 1994, (which application is incorporated herein by reference) a method of placing pin register hole markings on flexible printing plates is described. Briefly, in this method, the pin register hole markings are placed on original artwork used to create an image on the plate and the markings are carried through each step of the plate forming process until they are formed as a part of the raised image on each finished plate. The markings can take the form of an elongate line with a centrally located alignment cross-hair.
Once the finished plates are formed with the pin register hole markings imprinted thereon, pin register holes must be accurately punched or drilled in the plate material at the marking locations in order for the plates to be aligned on printing presses. In order to accomplish this, an apparatus and method was needed which was capable of steadily holding the finished plates for drilling. The apparatus needed to have an adjustable surface upon which the plates could be clamped and an optical alignment system was required to accurately adjust the surface. Finally, a drill or punch was required which could quickly and accurately create the requisite pin register holes on the clamped plate without distorting the plate material and without clogging the drill or punch.